Known in the past has been an internal combustion engine in which an exhaust passage is provided with an air-fuel ratio sensor, and an output of this air-fuel ratio sensor is used as the basis for feedback control of the amount of fuel fed to a combustion chamber of the internal combustion engine so that the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst becomes a target air-fuel ratio (for example, stoichiometric air-fuel ratio (14.6)).
In the internal combustion engine described in International Patent Publication No. 2014/118892A, an upstream side air-fuel ratio sensor is arranged at an upstream side of the exhaust purification catalyst in the exhaust flow direction, while a downstream side air-fuel ratio sensor is arranged at a downstream side of the exhaust purification catalyst in the exhaust flow direction. In this internal combustion engine, a target air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst is switched between a rich set air-fuel ratio richer than the stoichiometric air-fuel ratio and a lean set air-fuel ratio leaner than the stoichiometric air-fuel ratio. For example, the target air-fuel ratio is switched from the rich set air-fuel ratio to the lean set air-fuel ratio when the air-fuel ratio detected by the downstream side air-fuel ratio sensor has become a rich judged air-fuel ratio richer than the stoichiometric air-fuel ratio or has become less. Further, the target air-fuel ratio is switched from the lean set air-fuel ratio to the rich set air-fuel ratio when the air-fuel ratio detected by the downstream side air-fuel ratio sensor becomes higher than the rich judged air-fuel ratio and an estimated value of an oxygen storage amount of the exhaust purification catalyst becomes a predetermined switching reference storage amount or more.